It is necessary to bleed vehicle hydraulic systems during the vehicle assembly process. The bleeding is usually completed on the vehicle assembly line using vacuum bleeding equipment, which creates a vacuum within the sealed hydraulic system. The system is then vented to a hydraulic fluid, and atmospheric pressure forces the hydraulic fluid into the system. Fluid may also be forced into the system under pressure. Equipment such as this can reduce the time to complete the bleeding process, which correspondingly speeds up the assembly line and decreases the cost of vehicle production. It may also eliminate air pockets from difficult to bleed places. Typically, the vacuum will be applied to the hydraulic reservoir (or tank), which is necessarily readily acceptable due to the requirement of checking the fluid level, and topping up as necessary in service. During vacuum bleeding, direct access is not required to bleed nipples located at the brake slave cylinders, often located adjacent respective wheels.
Thus, vacuum bleeding is particularly applicable for use on a vehicle assembly line, though is less applicable for in service use, since the equipment required to vacuum bleed is expensive.
Problems can arise during vacuum bleeding if any component of the hydraulic system is not fully sealed from the atmosphere. Particular problems arise when using complex hydraulic or vacuum boosters in the system. Some systems use spool valves that may create a leak path from the atmosphere during the bleeding operation. A sufficient vacuum sometimes cannot be held because of leak paths, which cause inefficient bleeding. The leak paths need to be plugged to maintain a vacuum. This additional step increases the time of the bleeding process, which correspondingly slows down the assembly line and increases the cost of vehicle production. Furthermore, where the system is connected to a hydraulic pump, the pump itself is incapable of holding a sufficient vacuum. Thus, either air can be sucked through the pump when the pump has not been hydraulically primed, or alternatively hydraulic fluid can be sucked through the pump (when it has been hydraulically primed), creating a danger that the hydraulic fluid will enter and contaminate the vacuum bleeding equipment.
It is an aim of the present invention to overcome the problems described above by providing a device placed in an hydraulic system to isolate a potential leak path so that a vacuum can be held during bleeding. The evacuated part of the system can then be filled with hydraulic fluid.
It is a further aim of the invention to eliminate the step of plugging a potential leak path. Plugging requires human intervention, which introduces a potential source of mistakes and increases the time to complete the vacuum bleeding operation because the plug must be removed.